The present invention generally relates to a method for manufacturing zinc oxide whiskers, and more particularly, to a method for manufacturing zinc oxide whiskers in uniform shape wherein each whisker is formed in a crystalline body composed of a core part and an acicular part extending not smaller than several tm long in four different directions from said core part (this structure of a whisker is hereinafter referred to as a specific shape).
At present, zinc oxide generally used as an industrial material is manufactured by a so-called French method in many cases. According to this French method, zinc oxide results in a dumpling aggregate of particles not uniform in size and particularly in shape. Although another method is known to produce zinc oxide in particles of slender and short aciculae with high yield (for example, disclosed in Japanese Patent Publication No. 60-5529 (5529/1985), this method is a revised version of the above French method, whereby steam of heated zinc is led outside a furnace and cooled rapidly, without achieving a huge crystalline body, but forming an acicular crystal of a very small size (0.1-15 tm long).
The acicular crystals obtained in the above-described prior arts are smaller in size by approximately two digits than various types of industrial whiskers presently in the market. Therefore, the prior art acicular crystals show no particular difference from the dumpling zinc oxide in terms of reinforcing effect for metals, ceramics, resins or the like. An outstanding reinforcing effect of whisker is not found in the prior art acicular particles. Meanwhile, a whisker consisting of a single crystal in fibrous structure has a remarkably high mechanical strength as compared with the dumpling substance of the same material, and accordingly drawing attention as a reinforcing material to obtain great mechanical strength in mixture with the other substance, and nowadays, various kinds of whiskers composed of, for example, metal, metal oxide, metal carbide, metal nitride, etc. are sold for industrial use. Moreover, although a whisker of zinc oxide having the length in mm digit is also known (Japanese Patent Laid-open Publication No. 50-5597 (5597/1975) which is the size of a simple acicula, the whisker disclosed in this prior art is manufactured from an alloy of zinc, and therefore impurities are included in the crystal, or a substrate is indispensable during the growth of the crystal at a position far from the material, with the other inconveniences being noted in the manufacture. That is, a complicated structure of the device for the manufacture, a long-time operation with low yield, etc. still remain to be solved. In other words, most of the prior art whiskers are within the range of experimental studies.